261-c# base64的文件内容保存为文件、下载pdf文件（内部）

string pdfPath = System.IO.Path.Combine(savePath, fileName);
string pdfStr = JsonUtils.GetValue("pdfStr", item);
byte[] pdfBytes = Convert.FromBase64String(pdfStr);
File.WriteAllBytes(pdfPath, pdfBytes);

下载pdf文件：

        /// <summary>
        /// 下载pdf文件
        /// </summary>
        /// <param name="requestParams"></param>
        /// <param name="url"></param>
        /// <param name="cookies"></param>
        /// <param name="pdfPath"></param>
        /// <returns></returns>
        private static ReturnValue<string> downloadPDF(Dictionary<string,object> requestParams,string url,string cookies,string pdfPath) 
        {
            ReturnValue<string> rs_pdf = new ReturnValue<string>();
            // 设置要下载的PDF文件的URL

            // 创建一个 HttpClient 实例，并配置 CookieContainer 以管理 Cookies
            var cookieContainer = new CookieContainer();
            var handler = new HttpClientHandler
            {
                CookieContainer = cookieContainer,
                UseCookies = true
            };

            var rs_ck = CookieChangeTools.GetCookieCollectionFromXQYCookieString(cookies);


            using (HttpClient httpClient = new HttpClient(handler))
            {
               
                cookieContainer.Add(rs_ck.Value);
                // 使用 Newtonsoft.Json 库将参数对象转换为 JSON 字符串
                string jsonParams = Newtonsoft.Json.JsonConvert.SerializeObject(requestParams);

                // 创建 HTTP 请求的内容
                var content = new StringContent(jsonParams, System.Text.Encoding.UTF8, "application/json");

                try
                {
                    // 使用 Task.Run 在后台线程执行下载操作
                    Task.Run(async () =>
                    {
                        // 发送 POST 请求，传递参数
                        HttpResponseMessage response = await httpClient.PostAsync(url, content);

                        // 检查响应是否成功
                        if (response.IsSuccessStatusCode)
                        {
                            // 读取响应内容作为字节数组
                            byte[] pdfBytes = await response.Content.ReadAsByteArrayAsync();

                            System.IO.File.WriteAllBytes(pdfPath, pdfBytes);
                            rs_pdf.Value = pdfPath;
                            rs_pdf.Success = true;
                        }
                        else
                        {
                            rs_pdf.Success = false;
                            rs_pdf.Msg = "下载PDF文件时发生错误，HTTP 状态码：" + response.StatusCode;
                        }
                    }).Wait(); // 等待后台任务完成
                }
                catch (Exception ex)
                {
                    rs_pdf.Success = false; 
                    rs_pdf.Msg = "下载PDF文件时出错：" + XqdClass.Tools.GetExceptionMsg(ex);
                }
            }

            return rs_pdf;
        }